The control of the drive undergoes continuous development with the objective of reducing the fuel consumption and exhaust-gas emissions of motor vehicles. A highly promising possibility for saving fuel involves interrupting the flow of power in the drive train in suitable driving situations and then temporarily operating the vehicle in a rolling mode with the drive engine rotating at idle speed, or even also turning off the drive engine and moving the vehicle in a so-called freewheel mode. These functions are already known.
A problematic aspect thereof, however, is that the detection mechanisms conventionally used to determine driving situations that are suitable for the freewheel mode or rolling mode, which rely primarily on evaluations of vehicle resistance and the roadway gradient, the movements of the gas pedal and the brake pedal, the current speed range, and vehicle acceleration, are often inadequate for always utilizing the freewheel/rolling mode in a reliable and expedient manner.
In particular, in the known control methods for a freewheel mode or rolling mode, the vehicle surroundings and the vehicle state are not always interpreted correctly using a sensor system available in the vehicle, due to a somewhat unfiltered or incomplete accounting for information on consumption-relevant variables and/or due to complex, partially contradictory influences, which can result in unnecessary and counterproductive neutral shiftings or interruptions in the flow of power in the drive train.
Furthermore, it is known to equip modern vehicles with automatic vehicle speed control functions or vehicle speed functions and distance control functions to an increasing extent, for reasons of comfort, traffic, and vehicle safety. Such systems are already available for passenger vehicles and commercial vehicles, for instance as a Tempomat unit (cruise control) which brings about or maintains a desired speed specified by the driver or, as an expansion thereof, as ACC (Adaptive Cruise Control) or ADR (Automatic Distance Regulation) which establish a monitoring region in front of the vehicle or around the vehicle using sensors such as radar, infrared, video, or ultrasound, whereby the distance, at the least, from the vehicle traveling directly in front is also adjusted via automatic deceleration or braking by means of an autonomous braking system (Bremsomat unit (brake control unit)).
DE 10 2004 017 115 A1 makes known a method for the automatic driving speed control and distance control for a vehicle comprising an automatic or automated transmission, in which the driving speed can be varied within the range of a preselected target speed. In that particular case, an acceleration phase is followed by a roll-out phase in which the flow of power in the drive train can be interrupted to save fuel. Topographical data, data from a monitoring device pertaining to the immediate vehicle surroundings, and/or vehicle parameters can be taken into account via a navigation device in the sequence of acceleration and roll-out phases. The acceleration phases can be supported by an electric motor which is present in addition to an internal combustion engine.
The known method uses a freewheel mode or rolling mode to control speed within a Tempomat unit or ACC system. The disadvantage thereof is that an independently controllable freewheel mode or rolling mode is not provided. In particular, neutral shiftings or engine shut-offs are bound to the requirements of the Tempomat unit or the Bremsomat unit. The possibilities for use of the freewheel mode or rolling mode are therefore somewhat limited.
DE 102 21 701 A1 makes known a control method for a motor vehicle comprising an automatic transmission, in which a clutch is disengaged, thereby interrupting the flow of power in the drive train if a gas pedal or a brake pedal, or actuating variables having like effect, are not actuated while the engine is running and the vehicle is traveling at a minimum driving speed. After the clutch is disengaged, the transmission is shifted into neutral and the vehicle is therefore in a rolling mode. When the gas pedal or the brake pedal is actuated, or variables having like effect are changed, the clutch is re-engaged, thereby terminating the rolling mode. Before the clutch is engaged, rotational speed synchronization takes place between the driving internal combustion engine and a drive shaft in order to terminate the rolling mode as comfortably and rapidly as possible. It is also provided that the clutch will not be disengaged and, therefore, the rolling mode will not be activated, if vehicle deceleration is imminent. This can be detected in the form of downhill driving or a rapid release of the gas pedal.
The disadvantage thereof is that a freewheel mode or rolling mode is not always appropriate when the vehicle is neither traveling downhill nor the gas pedal or brake pedal is actuated. In particular, prognostic parameters related to topography or the traffic situation, or that are internal to the vehicle are not taken into consideration in the method. In addition, a combined freewheel and rolling mode is not provided with a Tempomat unit or Bremsomat unit.
WO 2003/037 672 A1 makes known a multi-speed transmission, in particular for heavy commercial vehicles, which is shifted into neutral, i.e. into a rolling mode, when a low-consumption driving state is detected. A low-consumption driving state is detected and the neutral position is attained via shifting when a target speed is specified and the driving speed would decrease without the rolling mode. This is assumed, in particular, when neither the gas pedal nor the brake pedal are actuated, and equivalent variables do not change. A supplemental brake system which can be actuated in the rolling mode is provided for safety reasons. The gear that is currently engaged is also taken into consideration. The disadvantage thereof is that a prognostic evaluation of the rolling mode is not provided, and therefore unfavorable neutral shiftings can be triggered.